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MoO3-based HDS catalyst obtained by the polymeric precursor method
Materials Letters 60 (2006) 2638 – 2641 www.elsevier.com/locate/matlet
MoO3-based HDS catalyst obtained by the polymeric precursor method Luiza G. Pereira a , Antonio S. Araujo b,⁎, Marcelo J.B. Souza c , Anne M.G. Pedrosa b , Maria Rita C. Santos a , Iêda M.G. Santos a , Luiz E.B. Soledade a , Antonio G. Souza a b
a Universidade Federal da Paraíba, Departamento de Química, CEP 58059-900, João Pessoa, PB, Brazil Universidade Federal do Rio Grande do Norte, Departamento de Química, CEP 1662, 59078-970, Natal, RN, Brazil c Universidade Federal de Sergipe, Departamento de Engenharia Química, 49.100-000, São Cristovão, SE, Brazil
Received 10 October 2005; accepted 21 January 2006 Available online 9 February 2006
Abstract The NiCoMo/γ-Al2O3 catalyst was synthesized by polymeric precursor method and it was structurally and morphologically characterized by X-ray diffraction, infrared spectroscopy, nitrogen adsorption measurements. Besides the structural and morphological characterization, a catalytic performance test for the hydrodesulfurization process (HDS) using thiophene was also carried out, in a continuous flow reactor. The method proposed for the synthesis of such a catalyst led to an excellent performance of the HDS process, converting more than 97% of thiophene into isobutane, 1-butene, n-butane, trans-2-butene and cis-2-butene. © 2006 Published by Elsevier B.V. Keywords: MoO3; HDS; Thiophene; γ-Al2O3; Polymeric precursor method
1. Introduction The environmental problems related to sulfur in the fuels has led Brazil to decrease the sulfur level of diesel oil since 90s. Further cuts are foreseen and progresses have been achieved aiming at diminishing the pollution by means of treating the oil of heaviest fractions with the HDS process. The requirements of the actual environmental laws recommend a very big sulfur reduction, which is hardly feasible by the conventional technology, as it is required a 95% sulfur conversion. Therefore, there is many interest on to study the desulfurization process and more efficient catalysts, able to lead to the effective removal of all sulfur compounds [1–4]. All industrial hydrotreating catalysts contain at least two elements of the groups VI and VIII of the periodic table [5]. The MoO3-based catalysts are basically used for the HDS reaction of fuels, mainly when doped with nickel or cobalt and anchored on the surface of inert supports [6]. Cobalt species facilitate the hydrogenation of sulfur atoms adsorbed on the HDS active sites (sites of partially coordinated molybdenum atoms) as they ⁎ Corresponding author. Tel.: +55 84 3211 9240. E-mail address: [email protected] (A.S. Araujo). 0167-577X/$ - see front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.matlet.2006.01.055
promote a rotation in the hydrogen molecules and consequently accelerate the HDS reaction [7,8]. A few articles in the literature investigate the reaction mechanisms and present the catalyst performance in the HDS desulfurization process of sulfurcontaining compounds, such as aromatic compounds [9]. The main objective of the present study is to investigate the influence of the molybdenum-based catalyst synthesized by polymeric precursor method [10] on HDS process. This method was proposed once it presents several advantages as compared with other methods, such as high stoichiometric control, purity, reproducibility and homogeneity [10,11]. Both the supported and unsupported catalysts were characterized using the techniques of XRD, infrared spectroscopy and its surface area was determined. The techniques of XRD and infrared spectroscopy were used to characterize the structural evolution of the system. The catalytic activity in the HDS process for the thiophene desulfurization was evaluated utilizing a continuous flow reactor. 2. Experimental The catalyst Ni0.005Co0.005Mo0.99O3/γ-Al2O3 (NiCoMo/γAl2O3) was synthesized by the polymeric precursor method, a
L.G. Pereira et al. / Materials Letters 60 (2006) 2638–2641
soft synthesis method with the advantages of high homogeneity at the molecular level, low synthesis temperature, good stoichiometric control, and yielding ultrafine particles. [10– 12]. So, a water solution was prepared with citric acid and stoichiometric amounts of ammonium molybdate, cobalt acetate and nickel acetate. The molar ratio between citric acid and all the metal cations (Ni, Co and Mo) was set at 3 : 1. To this solution, ethylene glycol was added at the citric acid/ethylene glycol mass proportion of 60 : 40. This resulting solution, a resin, was maintained at 90 °C for a time period less than 30 min. A part of this resin was calcined at 500 °C and the other part was used for the impregnation of the metallic ions within the γ-Al2O3 support. After the impregnation on the γ-Al2O3, a thermal treatment in ambient atmosphere was carried out aiming at the elimination of the organic material at 500 °C. The heat treated powder was characterized by XRD, FTIR and its surface area was determined by BET method. The structural evolution was observed by low-angle XRD using the Cu Kα radiation (λ[Kα1(Cu)] = 1.54178 Å) in a RIGAKU D2500 equipment employing a voltage of 30 kV and
Fig. 1. XRD diffraction patterns of the NiCoMo catalyst: (A) before the impregnation in γ-Al2O3 and (B) after the impregnation in γ-Al2O3.
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Fig. 2. Infrared vibration spectra of the NiCoMo/γ-Al2O3 catalyst. The infrared spectra of the γ-Al2O3 and MoO3 pure oxides are also displayed for comparison.
current of 30 mA, with a Ni filter. This analysis was carried out at the 10° ≤ 2θ ≤ 60° range, with a goniometer speed of 2° min− 1 and a step size of 0.02°. The vibrations of the catalyst were analyzed by infrared absorption spectroscopy, by means of the KBr pellet method, utilizing a model MB-102 Bomem spectrophotometer, at the wave number range from 1400 to 400 cm− 1. The specific surface area was determined by nitrogen adsorption, according to the Brunauer–Emmett– Teller (BET) method. The suitability of the catalyst for the HDS process was assessed by means of a pilot desulfurization test using the HDS process. Thiophene was utilized as a representative sulfur containing compound of gasoline. For the catalyst test, a continuous flow of thiophene vapor was fed into a 12 mminternal diameter quartz microreactor, containing an amount of approximately 100 mg of the catalyst. Prior to the HDS test, the oxide catalysts were previously heated up to 350 °C at a heating rate of 10 °C min− 1 in a 45 mL min− 1 dynamic flow of hydrogen, maintaining this temperature
Fig. 3. Selectivity of the compounds obtained from the thiophene degradation over the NiCoMo/γ-Al2O3 catalyst.
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L.G. Pereira et al. / Materials Letters 60 (2006) 2638–2641
Table 1 Conversion degree of thiophene in n-heptane and selectivity of the degradation products over NiCoMo/γ-Al2O3 catalyst as a function of reaction time Time (min)
Conversion (%)
Selectivity (%) iso-butane
1-butene
n-butane
2-butene-trans
2-butene-cis
15 30 45 60 75
96.7 96.7 97.1 95.6 95.8
25.2 22.2 19.2 22.1 20.9
21.6 23.5 24.0 25.9 27.0
1.3 2.4 9.0 1.4 4.1
21.0 21.2 20.7 21.3 19.7
30.9 30.6 27.2 29.3 28.4
for 1 h. A saturator at 28 °C was loaded with a blend of thiophene (12,073 ppm–0.48% of sulfur) in n-heptane. This blend was carried through the reactor by a 45 mL min− 1 hydrogen flow at 1 atm pressure and 350 °C. The H2/thiophene blend molar ratio used in the test was 8:2. The catalyst test products were automatically injected by means of a 10-way valve at 15-min intervals to be analyzed in a Varian CP3800 gas chromatograph, equipped with a 60 m-megabore fused silica column, using a of thermal conductivity detector. 3. Results and discussion Fig. 1 shown XRD diffraction patterns of the NiCoMo catalyst before the impregnation in γ-Al2O3 (Fig. 1A) and after the impregnation in γ-Al2O3 (Fig. 1B). For comparison, in the Fig. 1A it can also be seen the XRD diffraction pattern for the MoO3 pure which displayed the diffraction peaks characteristic of both monoclinic αMoO3 and orthorhombic β-MoO3. The main peaks observed in the NiCoMo catalyst before the impregnation in γ-Al2O3 (Fig. 1A) are related to both MoO3 phases (α-MoO3 and β-MoO3). However, secondary phases also were detected, which were ascribed to both nickel and cobalt molybdates. The γ-Al2O3-supported catalyst (Fig. 1B) was also characterized by means of XRD. Only wide γ-Al2O3 bands [13] and low-intensity MoO3 peaks were observed. The presence of these phases in the supported catalyst, after the impregnation by the Mo-containing resin, is a strong indication that the molybdenum oxide is actually deposited on the γ-Al2O3 surface and does not form an extensive solid solution with alumina. Fig. 2 presents the infrared spectra of the NiCoMo/γ-Al2O3 supported catalyst after being submitted to heat treatments at 500 °C. For comparison, Fig. 2 also displays the infrared spectra of the pure oxides γ-Al2O3 and MoO3. For the γ-Al2O3 sample, a band is observed at 1070 cm− 1, which is indicative of the Al_O double-bond stretching vibration [14]. Bands between 487 and 614 cm− 1, indicative of interactive vibrations of the complexes AlO4 and AlO6 with isolated AlO6 octahedral groups, are observed. Similarly, at the vibration frequencies in the range from 746 to 860 cm− 1 are noticed bands that are also indicative of interactive vibrations of the compounds AlO4 and AlO6, but in this case with isolated tetrahedral groups, AlO4 [15]. The MoO3 infrared spectrum shows a vibration band at 985 cm− 1, ascribed to hexavalent Mo_O double-bond. The wide band from 850 to 950 cm− 1 indicates different Mo–O single bonds, with hexavalent and pentavalent molybdenum and in some cases tetravalent molybdenum. The wide bands peaked at 862, 817 and 567 cm− 1 correspond to the oxygen atom vibrations in Mo–O–Mo, in which Mo represents hexavalent molybdenum [16–19]. The bands due to the O–Mo–O deformation mode are noticed in the range from 500 to 371 cm− 1 in the MoO3 infrared spectrum [20]. Upon the formation of the NiCoMo films on γ-Al2O3, a quite wide band is observed between 900 and 400 cm− 1, indicating an overlapping between the alumina and the
molybdenum trioxide bands. It is also noted another band at 1090 cm− 1, indicative of the Al_O stretching vibration mode [14]. The total surface area of the NiCoMo/γ-Al2O3 catalysts, calculated according to the BET method, was 270 m2 g− 1. The catalytic activity of the NiCoMo/γ-Al2O3 was tested on HDS process. CG-MS analyses showed that the reaction products consisted of butanes and butenes. These results are summarized in Fig. 3 and Table 1. The presence of butane, iso-butene and butenes as reaction products suggest that due acid characteristics of the support were obtained products originating from the catalytic cracking. The dependence of thiophene selectivity on NiCoMo/γ-Al2O3 catalyst with the reaction time is also shown in Fig. 3. In accordance with these results it is possible to see that the selectivity is little influenced by contact reaction time. Table 1 shown the degree of conversion on function of reaction time. The NiCoMo/γ-Al2O3 catalyst showed a very high initial conversion (96.7%), which slightly decreases during the catalytic test, reaching, after 75 minutes, a final conversion of 95.8%. This fact might be associated to de-activation phenomena that took place along the reaction time, which are related to coke deposition.
4. Conclusions The polymeric precursor method is an excellent rout for synthesis of molybdenum-based catalyst supported on γalumina. XRD indicated that the catalyst supported consist mainly of the MoO3 phase supported on γ-Al2O3. The surface area of the supported catalyst studied was of 270 m2 g− 1. The NiCoMo/γ-Al2O3 catalyst obtained displayed a high catalytic performance in terms of conversion, over 95%, and also in terms of the selectivity of the obtained products: iso-butane, 1butene, n-butane, 2-butene-trans and 2-butene-cis. Acknowledgements This work was partially supported by the Brazilian researchfinancing institution CNPq. References [1] I. Mochida, K. Sakanishi, X. Ma, S. Nagao, T. Isoda, Catalysis Today 29 (1996) 185–189. [2] K.G. Knudsen, B.H. Cooper, H. Topsoe, Applied Catalysis. A, General 189 (1999) 205–215. [3] T.I. Korányi, M. Dobrovolszky, T. Koltai, K. Matusek, Z. Paál, P. Tétényi, Fuel Processing Technology 61 (1999) 55–71. [4] W.R.A.M. Robinson, J.A.R. Van Veen, V.H.J. De Beer, R.A. Van Santen, Fuel Processing Technology 61 (1999) 89–101. [5] P. Grange, X. Vanhaeren, Catalysis Today 36 (1997) 375–391. [6] F. Wypych, Química Nova 25 (2002) 83–88.
L.G. Pereira et al. / Materials Letters 60 (2006) 2638–2641 [7] H. Topsoe, B.S. Clausen, T. Nozaki, Applied Cataysis. A, General 163 (1997) 217–225. [8] V.M. Kogan, N.N. Rozhdestvenskaya, I.K. Korshevets, Applied Catalysis. A, General 234 (2002) 207–219. [9] H.R. Reinhoudt, R. Troost, A. Van Langeveld, D. Sie, S.T. Van Veen, J.A. R. Moulijn, Fuel Processing Technology 61 (1999) 133–147. [10] Pechini, M.P. U.S. Patent 3,330,697, July 11, 1967. [11] Paskocimas, C.A., Leite, E.R., Antunes, A.C., Longo, E., Varela, J.A. Morphological Characterization of Oxide Ceramic Powders Obtained by the Polymeric Precursors Method. In: P. Vincenzini. (Org.). Ceramics: Chatting the Future., 1995,1435–1442. [12] P.A. Lessing, Ceramic Bulletin 68 (1989) 1002–1007.
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[13] X. Carrier, J.F. Lambert, S. Kuba, H. Knözinger, C. Michel, Journal of Molecular Structure 656 (2003) 231–238. [14] S. Ram, Infrared Physics and Technology 42 (2001) 547–560. [15] J.M. Saniger, Materials Letters 22 (1995) 109–113. [16] L. Seguin, M. Figlarz, R. Cavagnat, J.C. Lasseguies, Spectrochimica Acta. Part A 51 (1995) 1323–1344. [17] W. Dong, A.N. Mansou, B. Dunn, Solid State Ionics 144 (2001) 31–40. [18] J. Lua, L. Gaoa, J. Guoa, K. Niiharab, Materials Research Bulletin 35 (2000) 2387–2396. [19] T.C. Xiao, A.P.E. York, H. Al-Megren, C.V. Williams, H.T. Wang, M.L.H. Green, Journal of Catalysis 202 (2001) 100–109. [20] S.A. Halawy, A. Mohamed, Thermochimica Acta 345 (2000) 157–164.
MoO3-based HDS catalyst obtained by the polymeric precursor method Luiza G. Pereira a , Antonio S. Araujo b,⁎, Marcelo J.B. Souza c , Anne M.G. Pedrosa b , Maria Rita C. Santos a , Iêda M.G. Santos a , Luiz E.B. Soledade a , Antonio G. Souza a b
a Universidade Federal da Paraíba, Departamento de Química, CEP 58059-900, João Pessoa, PB, Brazil Universidade Federal do Rio Grande do Norte, Departamento de Química, CEP 1662, 59078-970, Natal, RN, Brazil c Universidade Federal de Sergipe, Departamento de Engenharia Química, 49.100-000, São Cristovão, SE, Brazil
Received 10 October 2005; accepted 21 January 2006 Available online 9 February 2006
Abstract The NiCoMo/γ-Al2O3 catalyst was synthesized by polymeric precursor method and it was structurally and morphologically characterized by X-ray diffraction, infrared spectroscopy, nitrogen adsorption measurements. Besides the structural and morphological characterization, a catalytic performance test for the hydrodesulfurization process (HDS) using thiophene was also carried out, in a continuous flow reactor. The method proposed for the synthesis of such a catalyst led to an excellent performance of the HDS process, converting more than 97% of thiophene into isobutane, 1-butene, n-butane, trans-2-butene and cis-2-butene. © 2006 Published by Elsevier B.V. Keywords: MoO3; HDS; Thiophene; γ-Al2O3; Polymeric precursor method
1. Introduction The environmental problems related to sulfur in the fuels has led Brazil to decrease the sulfur level of diesel oil since 90s. Further cuts are foreseen and progresses have been achieved aiming at diminishing the pollution by means of treating the oil of heaviest fractions with the HDS process. The requirements of the actual environmental laws recommend a very big sulfur reduction, which is hardly feasible by the conventional technology, as it is required a 95% sulfur conversion. Therefore, there is many interest on to study the desulfurization process and more efficient catalysts, able to lead to the effective removal of all sulfur compounds [1–4]. All industrial hydrotreating catalysts contain at least two elements of the groups VI and VIII of the periodic table [5]. The MoO3-based catalysts are basically used for the HDS reaction of fuels, mainly when doped with nickel or cobalt and anchored on the surface of inert supports [6]. Cobalt species facilitate the hydrogenation of sulfur atoms adsorbed on the HDS active sites (sites of partially coordinated molybdenum atoms) as they ⁎ Corresponding author. Tel.: +55 84 3211 9240. E-mail address: [email protected] (A.S. Araujo). 0167-577X/$ - see front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.matlet.2006.01.055
promote a rotation in the hydrogen molecules and consequently accelerate the HDS reaction [7,8]. A few articles in the literature investigate the reaction mechanisms and present the catalyst performance in the HDS desulfurization process of sulfurcontaining compounds, such as aromatic compounds [9]. The main objective of the present study is to investigate the influence of the molybdenum-based catalyst synthesized by polymeric precursor method [10] on HDS process. This method was proposed once it presents several advantages as compared with other methods, such as high stoichiometric control, purity, reproducibility and homogeneity [10,11]. Both the supported and unsupported catalysts were characterized using the techniques of XRD, infrared spectroscopy and its surface area was determined. The techniques of XRD and infrared spectroscopy were used to characterize the structural evolution of the system. The catalytic activity in the HDS process for the thiophene desulfurization was evaluated utilizing a continuous flow reactor. 2. Experimental The catalyst Ni0.005Co0.005Mo0.99O3/γ-Al2O3 (NiCoMo/γAl2O3) was synthesized by the polymeric precursor method, a
L.G. Pereira et al. / Materials Letters 60 (2006) 2638–2641
soft synthesis method with the advantages of high homogeneity at the molecular level, low synthesis temperature, good stoichiometric control, and yielding ultrafine particles. [10– 12]. So, a water solution was prepared with citric acid and stoichiometric amounts of ammonium molybdate, cobalt acetate and nickel acetate. The molar ratio between citric acid and all the metal cations (Ni, Co and Mo) was set at 3 : 1. To this solution, ethylene glycol was added at the citric acid/ethylene glycol mass proportion of 60 : 40. This resulting solution, a resin, was maintained at 90 °C for a time period less than 30 min. A part of this resin was calcined at 500 °C and the other part was used for the impregnation of the metallic ions within the γ-Al2O3 support. After the impregnation on the γ-Al2O3, a thermal treatment in ambient atmosphere was carried out aiming at the elimination of the organic material at 500 °C. The heat treated powder was characterized by XRD, FTIR and its surface area was determined by BET method. The structural evolution was observed by low-angle XRD using the Cu Kα radiation (λ[Kα1(Cu)] = 1.54178 Å) in a RIGAKU D2500 equipment employing a voltage of 30 kV and
Fig. 1. XRD diffraction patterns of the NiCoMo catalyst: (A) before the impregnation in γ-Al2O3 and (B) after the impregnation in γ-Al2O3.
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Fig. 2. Infrared vibration spectra of the NiCoMo/γ-Al2O3 catalyst. The infrared spectra of the γ-Al2O3 and MoO3 pure oxides are also displayed for comparison.
current of 30 mA, with a Ni filter. This analysis was carried out at the 10° ≤ 2θ ≤ 60° range, with a goniometer speed of 2° min− 1 and a step size of 0.02°. The vibrations of the catalyst were analyzed by infrared absorption spectroscopy, by means of the KBr pellet method, utilizing a model MB-102 Bomem spectrophotometer, at the wave number range from 1400 to 400 cm− 1. The specific surface area was determined by nitrogen adsorption, according to the Brunauer–Emmett– Teller (BET) method. The suitability of the catalyst for the HDS process was assessed by means of a pilot desulfurization test using the HDS process. Thiophene was utilized as a representative sulfur containing compound of gasoline. For the catalyst test, a continuous flow of thiophene vapor was fed into a 12 mminternal diameter quartz microreactor, containing an amount of approximately 100 mg of the catalyst. Prior to the HDS test, the oxide catalysts were previously heated up to 350 °C at a heating rate of 10 °C min− 1 in a 45 mL min− 1 dynamic flow of hydrogen, maintaining this temperature
Fig. 3. Selectivity of the compounds obtained from the thiophene degradation over the NiCoMo/γ-Al2O3 catalyst.
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L.G. Pereira et al. / Materials Letters 60 (2006) 2638–2641
Table 1 Conversion degree of thiophene in n-heptane and selectivity of the degradation products over NiCoMo/γ-Al2O3 catalyst as a function of reaction time Time (min)
Conversion (%)
Selectivity (%) iso-butane
1-butene
n-butane
2-butene-trans
2-butene-cis
15 30 45 60 75
96.7 96.7 97.1 95.6 95.8
25.2 22.2 19.2 22.1 20.9
21.6 23.5 24.0 25.9 27.0
1.3 2.4 9.0 1.4 4.1
21.0 21.2 20.7 21.3 19.7
30.9 30.6 27.2 29.3 28.4
for 1 h. A saturator at 28 °C was loaded with a blend of thiophene (12,073 ppm–0.48% of sulfur) in n-heptane. This blend was carried through the reactor by a 45 mL min− 1 hydrogen flow at 1 atm pressure and 350 °C. The H2/thiophene blend molar ratio used in the test was 8:2. The catalyst test products were automatically injected by means of a 10-way valve at 15-min intervals to be analyzed in a Varian CP3800 gas chromatograph, equipped with a 60 m-megabore fused silica column, using a of thermal conductivity detector. 3. Results and discussion Fig. 1 shown XRD diffraction patterns of the NiCoMo catalyst before the impregnation in γ-Al2O3 (Fig. 1A) and after the impregnation in γ-Al2O3 (Fig. 1B). For comparison, in the Fig. 1A it can also be seen the XRD diffraction pattern for the MoO3 pure which displayed the diffraction peaks characteristic of both monoclinic αMoO3 and orthorhombic β-MoO3. The main peaks observed in the NiCoMo catalyst before the impregnation in γ-Al2O3 (Fig. 1A) are related to both MoO3 phases (α-MoO3 and β-MoO3). However, secondary phases also were detected, which were ascribed to both nickel and cobalt molybdates. The γ-Al2O3-supported catalyst (Fig. 1B) was also characterized by means of XRD. Only wide γ-Al2O3 bands [13] and low-intensity MoO3 peaks were observed. The presence of these phases in the supported catalyst, after the impregnation by the Mo-containing resin, is a strong indication that the molybdenum oxide is actually deposited on the γ-Al2O3 surface and does not form an extensive solid solution with alumina. Fig. 2 presents the infrared spectra of the NiCoMo/γ-Al2O3 supported catalyst after being submitted to heat treatments at 500 °C. For comparison, Fig. 2 also displays the infrared spectra of the pure oxides γ-Al2O3 and MoO3. For the γ-Al2O3 sample, a band is observed at 1070 cm− 1, which is indicative of the Al_O double-bond stretching vibration [14]. Bands between 487 and 614 cm− 1, indicative of interactive vibrations of the complexes AlO4 and AlO6 with isolated AlO6 octahedral groups, are observed. Similarly, at the vibration frequencies in the range from 746 to 860 cm− 1 are noticed bands that are also indicative of interactive vibrations of the compounds AlO4 and AlO6, but in this case with isolated tetrahedral groups, AlO4 [15]. The MoO3 infrared spectrum shows a vibration band at 985 cm− 1, ascribed to hexavalent Mo_O double-bond. The wide band from 850 to 950 cm− 1 indicates different Mo–O single bonds, with hexavalent and pentavalent molybdenum and in some cases tetravalent molybdenum. The wide bands peaked at 862, 817 and 567 cm− 1 correspond to the oxygen atom vibrations in Mo–O–Mo, in which Mo represents hexavalent molybdenum [16–19]. The bands due to the O–Mo–O deformation mode are noticed in the range from 500 to 371 cm− 1 in the MoO3 infrared spectrum [20]. Upon the formation of the NiCoMo films on γ-Al2O3, a quite wide band is observed between 900 and 400 cm− 1, indicating an overlapping between the alumina and the
molybdenum trioxide bands. It is also noted another band at 1090 cm− 1, indicative of the Al_O stretching vibration mode [14]. The total surface area of the NiCoMo/γ-Al2O3 catalysts, calculated according to the BET method, was 270 m2 g− 1. The catalytic activity of the NiCoMo/γ-Al2O3 was tested on HDS process. CG-MS analyses showed that the reaction products consisted of butanes and butenes. These results are summarized in Fig. 3 and Table 1. The presence of butane, iso-butene and butenes as reaction products suggest that due acid characteristics of the support were obtained products originating from the catalytic cracking. The dependence of thiophene selectivity on NiCoMo/γ-Al2O3 catalyst with the reaction time is also shown in Fig. 3. In accordance with these results it is possible to see that the selectivity is little influenced by contact reaction time. Table 1 shown the degree of conversion on function of reaction time. The NiCoMo/γ-Al2O3 catalyst showed a very high initial conversion (96.7%), which slightly decreases during the catalytic test, reaching, after 75 minutes, a final conversion of 95.8%. This fact might be associated to de-activation phenomena that took place along the reaction time, which are related to coke deposition.
4. Conclusions The polymeric precursor method is an excellent rout for synthesis of molybdenum-based catalyst supported on γalumina. XRD indicated that the catalyst supported consist mainly of the MoO3 phase supported on γ-Al2O3. The surface area of the supported catalyst studied was of 270 m2 g− 1. The NiCoMo/γ-Al2O3 catalyst obtained displayed a high catalytic performance in terms of conversion, over 95%, and also in terms of the selectivity of the obtained products: iso-butane, 1butene, n-butane, 2-butene-trans and 2-butene-cis. Acknowledgements This work was partially supported by the Brazilian researchfinancing institution CNPq. References [1] I. Mochida, K. Sakanishi, X. Ma, S. Nagao, T. Isoda, Catalysis Today 29 (1996) 185–189. [2] K.G. Knudsen, B.H. Cooper, H. Topsoe, Applied Catalysis. A, General 189 (1999) 205–215. [3] T.I. Korányi, M. Dobrovolszky, T. Koltai, K. Matusek, Z. Paál, P. Tétényi, Fuel Processing Technology 61 (1999) 55–71. [4] W.R.A.M. Robinson, J.A.R. Van Veen, V.H.J. De Beer, R.A. Van Santen, Fuel Processing Technology 61 (1999) 89–101. [5] P. Grange, X. Vanhaeren, Catalysis Today 36 (1997) 375–391. [6] F. Wypych, Química Nova 25 (2002) 83–88.
L.G. Pereira et al. / Materials Letters 60 (2006) 2638–2641 [7] H. Topsoe, B.S. Clausen, T. Nozaki, Applied Cataysis. A, General 163 (1997) 217–225. [8] V.M. Kogan, N.N. Rozhdestvenskaya, I.K. Korshevets, Applied Catalysis. A, General 234 (2002) 207–219. [9] H.R. Reinhoudt, R. Troost, A. Van Langeveld, D. Sie, S.T. Van Veen, J.A. R. Moulijn, Fuel Processing Technology 61 (1999) 133–147. [10] Pechini, M.P. U.S. Patent 3,330,697, July 11, 1967. [11] Paskocimas, C.A., Leite, E.R., Antunes, A.C., Longo, E., Varela, J.A. Morphological Characterization of Oxide Ceramic Powders Obtained by the Polymeric Precursors Method. In: P. Vincenzini. (Org.). Ceramics: Chatting the Future., 1995,1435–1442. [12] P.A. Lessing, Ceramic Bulletin 68 (1989) 1002–1007.
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[13] X. Carrier, J.F. Lambert, S. Kuba, H. Knözinger, C. Michel, Journal of Molecular Structure 656 (2003) 231–238. [14] S. Ram, Infrared Physics and Technology 42 (2001) 547–560. [15] J.M. Saniger, Materials Letters 22 (1995) 109–113. [16] L. Seguin, M. Figlarz, R. Cavagnat, J.C. Lasseguies, Spectrochimica Acta. Part A 51 (1995) 1323–1344. [17] W. Dong, A.N. Mansou, B. Dunn, Solid State Ionics 144 (2001) 31–40. [18] J. Lua, L. Gaoa, J. Guoa, K. Niiharab, Materials Research Bulletin 35 (2000) 2387–2396. [19] T.C. Xiao, A.P.E. York, H. Al-Megren, C.V. Williams, H.T. Wang, M.L.H. Green, Journal of Catalysis 202 (2001) 100–109. [20] S.A. Halawy, A. Mohamed, Thermochimica Acta 345 (2000) 157–164.